Air fuel control for a PT fuel system

An air fuel control system for an internal combustion engine is disclosed. The control system includes an air pressure responsive device for modulating mechanically the flow of fuel into the engine in response to the pressure of air within the intake manifold. The pressure-responsive device includes first and second chambers, separated by a diaphragm being attached to a piston, with the first chamber which is connected to the intake manifold by an air line. The air fuel control system further includes a fuel metering device for controlling the flow of fuel into the air-fuel control in response to intake manifold air pressure including a barrel and plunger assembly with the barrel inlet port being specifically configured to accommodate both the no-air and transition-curve fuel rail pressures. The barrel profile is designed to meter fuel quickly and precisely in response to changes in manifold air pressure. Displacement of the plunger initially uncovers a small inlet port in the barrel which provides for viscosity insensitivity for aiding in cold starts and cold accelerations. Continued displacement of the plunger uncovers the lead of a transition region which provides for ease in the calibration of the air fuel control. A further region of transition region is next uncovered which permits acceleration with reduced acceleration smoke, noise and emissions while optimizing transient engine response. With an increase in air pressure from the manifold, a fourth region is uncovered which represents a driver feel of the acceleration without emission penalties and finally, once the plunger has reached the larger input port, a sharp inflection is realized wherein full fuel flow is permitted.